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1.
Twelve crossbred gilts, 169 ± 3 days of age and 72.8 ± 3.4 kg body weight, were hypophysial stalk-transected (HST)1 or sham hypophysial stalk-transected (S-HST). Gilts were ovariectomized 6 days later and assigned to four treatments of 3 gilts each in a 2 × 2 factorial arrangement. One-half of the HST and S-HST gilts received 5 mg estradiolbenzoate (EB) or corn oil vehicle im at 0800 hr daily for 5 days beginning 64 ± 3 days after HST or S-HST. Blood was collected by jugular vein cannula at 0830 and 0900 hr the day after the last injection of EB or oil. Immediately after the 0900 hr sample, 200 μg thyrotropin releasing hormone (TRH) were injected (iv). Mean basal serum prolactin (PRL) concentration was similar for HST (10.3 ± 1.0 ng/ml) and S-HST (12.3 ± 1.7 ng/ml) gilts, however mean basal serum PRL concentration was greater (P<.05) for EB-treated gilts (13.7 ± 1.3 ng/ml) than for oil-treated gilts (8.8 ± .5 ng/ml). Mean serum PRL concentration of all gilts increased within 10 min and returned to approximately 20 ng/ml by 150 min after TRH. Maximum serum PRL concentrations at 10 min after TRH were greater (P<.01) for S-HST (255.9 ± 29.6 ng/ml) than HST gilts (83.4 ± 18.8 ng/ml), but were not different for EB (198.0 ± 50.6 ng/ml) and oil-treated gilts (141.4 ± 36.3 ng/ml). Area under the serum PRL response curve after TRH was greater (P<.005) for S-HST than HST gilts and for EB than oil-treated gilts (P<.05). These results do not eliminate the possible influence of estrogen on PRL secretion at the hypothalamus, but do indicate that estrogen directly stimulated the anterior pituitary gland to secrete PRL.  相似文献   

2.
The physiological bases for differences in milk production between breeds of cattle selected for beef or milk production are largely unknown. This study was conducted to determine concentrations of prolactin (PRL) and growth hormone (GH) in serum before and after teat stimulation in primiparous Hereford and Holstein heifers. Blood was collected from 6 beef and 9 dairy heifers at 115, 175, 230 and 250 d of gestation. Sampling times were -15, -10, -5, 0, 2, 4, 6, 8, 10, 12, 15, 20, 25 and 30 min relative to test stimulation. Mean areas under PRL response curves for beef and dairy heifers at 115, 175, 230 and 250 d of gestation were 427, 447, 556, 273 and 243, 189, 167, 343 ng/ml/30 min, respectively. Calculations of area (but not basal levels) excluded instances when no PRL response to test stimulation was obtained (22%). Neither stage of gestation nor breed affected PRL response. Basal PRL did not differ between breeds and was 1.8, 2.6, 2.4 and 9.2 ng/ml at 115, 175, 230 and 250 d of gestation. GH did not differ between breeds and was 6.6, 6.2, 5.5 and 7.4 ng/ml at 115, 175, 230 and 250 d. No difference between breeds was apparent with regard to PRL or GH secretion during first gestation.  相似文献   

3.
In two experiments, 17-wk-old Holstein bulls exposed to 16 (Exp. 1) or 24 h (Exp. 2) of light daily were compared with bulls given 8 h of light. Blood was sampled at 30-min or 120-min intervals for 48 h at the beginning and again after 4 wk of light treatment. Melatonin concentrations varied episodically in serum, and means were 1.6-fold to 5.1-fold greater during darkness than during light periods. Continuous lighting abolished the nocturnal increase in concentrations of melatonin in three of four calves. Prolactin (PRL) was greater (P less than .05) in calves receiving 16 h (30.9 ng/ml of serum) than in calves receiving 8 h (7.0 ng/ml) of light daily. Prolactin was not different between calves receiving 24 or 8 h of light daily. In a third experiment, one pinealectomized (PX) and two sham PX (SPX) calves were exposed to continuous lighting and infused with melatonin for 16 h/d for 5 wk, and one PX and two SPX calves were infused for 8 h daily. Melatonin infusion increased average concentrations of melatonin in serum 7.2-fold to 18-fold above baseline concentrations. Duration of melatonin infusion did not affect PRL (21.0 vs 20.8 ng/ml of serum). Also, surgical treatment did not affect PRL concentrations. Similarly, in a fourth experiment, PRL in postpubertal heifers fed melatonin to mimic and 8L:16D photoperiod averaged 27.1 ng/ml of serum, which was not different from PRL in heifers receiving 16L:8D and fed vehicle (32.6 ng/ml). We conclude that PRL and melatonin are each affected by photoperiod but are not casually related in cattle.  相似文献   

4.
Fifteen mature cows and 12 two-year-old heifers were superovulated with purified follicle stimulating hormone (FSH-P) to study the relationship between FSH-P dose level and response (measured as number of palpated corpora lutea (CL) and plasma progesterone concentration). The cattle came from a high prolificacy breeding herd for which cows were originally purchased after producing at least two sets of twins; the heifers were bred in the herd. At dose levels of 8, 16, 24 and 28 mg FSH-P in cows, averages respectively of 2.3, 3.5, 6.9 and 11.1 palpable CLs were found. There was an average difference in response of two CLs between heifers and cows (higher in heifers, though not significantly so). The relationship found between progesterone concentration and CL number could be a useful indicator of superovulation success in future experiments. The regression for cows was 1.25±0.11 ng/ml progesterone per unit increase in CL number, with a correlation of 0.92 between the two variables over the CL range 1 to 25. The corresponding value for heifers was 2.74±0.24 ng/ml per CL (correlation 0.94), or 2.50±0.40 ng/ml per CL (correlation 0.83) if one record (29 CL, 84 ng progesterone/ml) was excluded.  相似文献   

5.
The effects of a serum gonadotropin (SG) superovulation hormonal preparation were investigated on catecholamine levels (norepinephrine, dopamine and epinephrine) in the blood plasma of ewes with synchronized oestrus in the oestrus period. In this trial the blood plasma of eleven ewes of the Slovak Merino breed was analyzed to detect catecholamines in the oestrus period. Superovulation was induced by an i.m. administration of 1500 IU SG as soon as oestrus synchronization with Agelin vaginal tampons finished (20 mg chlorsuperlutin) which lasted for 10 days. Catecholamines were detected in the blood plasma before synchronization, on the day of Agelin vaginal tampons application, and in 48 and 72 hours after the hormone administration--on the days of the expected ovulation. Catecholamine concentrations in the blood plasma were determined by a radioenzymatic assay using a Catechola test (Praha). The results indicate that synchronization and hormonal stimulation influence plasma catecholamine levels. The norepinephrine (NE) concentration in the blood plasma of the control samples has the value of 8.31 +/- 0.732 pmol/ml. An insignificant increase in the NE levels (13.12 +/- 0.120 pmol/ml; Fig. 1) was recorded on day 1 of the trial, after the start of synchronization. On the day of the expected ovulation the NE concentrations rose to 17.12 +/- 1.289 pmol/ml (P less than 0.001) and they remained significantly increased (P less than 0.01) at the level of 12.89 +/- 1.020 pmol/ml on the following day of the experiment. The dopamine level (DA) in the plasma of a control sample is 6.42 +/- 0.350 pmol/ml (Fig. 2).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

6.
Fifteen mature cows and 12 two-year-old heifers were superovulated with purified follicle stimulating hormone (FSH-P) to study the relationship between FSH-P dose level and response (measured as number of palpated corpora lutea (CL) and plasma progesterone concentration). The cattle came from a high prolificacy breeding herd for which cows were originally purchased after producing at least two sets of twins; the heifers were bred in the herd. At dose levels of 8,16, 24 and 28 mg FSH-P in cows, averages respectively of 2.3, 3.5, 6.9 and 11.1 palpable CLs were found. There was an average difference in response of two CLs between heifers and cows (higher in heifers, though not significantly so). The relationship found between progesterone concentration and CL number could be a useful indicator of superovulation success in future experiments. The regression for cows was 1.25 +/- 0.11 ng/ml progesterone per unit increase in CL number, with a correlation of 0.92 between the two variables over the CL range 1 to 25. The corresponding value for heifers was 2.74 +/- 0.24 ng/ml per CL (correlation 0.94), or 2.50 +/- 0.40 ng/ml per CL (correlation 0.83) if one record (29 CL, 84 ng progesterone/ml) was excluded.  相似文献   

7.
The influence of age, sex and castration on plasma concentrations of insulin-like growth factor-I (IGF-I) and other metabolic hormones related to growth was studied in cattle. Plasma was sampled from bulls, steers, heifers, and ovariectomized heifers at 20-min intervals for 12 hr at 5, 8, 12, and 15 mo of age. Plasma samples from each animal taken during each 12-hr period were composited for analysis of IGF-I, testosterone, total estrogens, thyroxine, triiodothyronine, insulin, and glucose. The mean plasma IGF-I concentration in all cattle increased from 61.6 to 158.6 ng/ml as the animals aged (p less than .01). Over all ages, bulls had greater concentrations of IGF-I than steers, heifers, or ovariectomized heifers (P less than .01). Bulls also had higher concentrations of testosterone (P less than .01) and total estrogens (P less than .01). Triiodothyronine concentration was greater in ovariectomized heifers than in bulls (P less than .01) or steers (P less than .05). Females had higher concentrations of thyroxine than males (P less than .01). Concentrations of triiodothyronine in the cattle were greater (P less than .01) during the winter and early spring as compared with the summer. Concentrations of insulin and glucose were not influenced by sex or castration; however, insulin increased in all cattle with age (P less than .01). The mean increase in IGF-I concentration with age within each of the four groups was associated with an increase in concentration of plasma insulin but the differences due to sex were not related to differences in insulin.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

8.
The effects of growth hormone-releasing peptide-6 (GHRP-6) on peripheral plasma concentrations of growth hormone (GH) and hypophysial portal plasma concentrations of growth hormone-releasing hormone (GHRH) and somatostatin (SRIF) were investigated in conscious ewes. Paired blood samples were collected from the hypophysial portal vessels and from the jugular vein of nine ewes for at least 2 hr. The sheep were then given a bolus injection of 10 μg of GHRP-6 per kg followed by a 2-hr infusion of GHRP-6 (0.1 μ/kg · hr). Blood sampling continued throughout the infusion and for 2 hr afterwards. An increase in plasma GH concentration was observed in the jugular samples of six of the nine ewes (1.4 ± 0.3 vs 7.4 ± 2.0 ng/ml, P < 0.05) 5–10 min after the GHRP-6 bolus injection, but in no case did we observe a significant coincident release of GHRH. During the infusion period, mean plasma GHRH levels were not significantly increased but there was a 50% increase (P < 0.05) in GHRH pulse frequency; GHRH pulse amplitude was not changed. Mean SRIF concentration, pulse frequency, and pulse amplitude were unchanged by GHRP-6 treatment. These data indicate that GHRP-6 causes a small, but significant effect on the pulsatile secretion of GHRH, indicating action at the hypothalamus or higher centers of the brain. The large initial GH secretory response to GHRP-6 injection does not appear to be the result of GHRP-6 action on GHRH or SRIF secretion.  相似文献   

9.
Ten gilts on day 6·11 of the estrous cycle (onset of estrus = day 0) were given 115 mg of naloxone (NAL), an opioid antagonist, in saline i.v. (n = 5) or saline Lv. (n = 5). Jugular blood was collected at 15 min intervals for 2 hr before and 4 hr after treatment. Serum LH concentrations were 0.4 ± 0.1 ng/ml before NAL treatment, increased (P<.01) to 4.3 ± 0.7 ng/ml at 15 min following NAL treatment and returned to control concentrations by 75 minutes. Serum PRL concentrations were 5.0 ± 0.1 ng/ml before NAL treatment, increased (P<.05) to 14.8 ± 2.9 ng/ml at 30 min following NAL treatment and returned to control concentrations by 120 minutes. Serum LH and PRL concentrations were 0.5 ± 0.1 ng/ml and 5.2 ± 0.4 ng/ml, respectively, at 15 min following saline treatment and remained unchanged throughout the blood sampling period. Four of the 5 NAL treated gilts responded with an increase in both serum LH and PRL concentrations. The mean of serum progesterone concentrations, quantitated in samples taken every 2 hr, were similar for controls (22.7 ± 1.8 ng/ml) and NAL (26.5 ± 1.4 ng/ml) treated gilts. The gilt which failed to respond to NAL had nondetectable concentrations of serum progesterone and was excluded from analysis. These data indicate that the opioids modulate LH and PRL secretion during the luteal phase of the estrous cycle.  相似文献   

10.
The aim of the present study was to investigate the changing profiles of plasma metabolic hormones during the ovarian cycles of beef and dairy cattle. We used 16 non-pregnant, non-lactating Japanese Black beef cattle (6 heifers and 10 cows; parity=2.3 +/- 0.8) and 12 multiparous Holstein dairy cows (parity=3.0 +/- 0.3). Blood samples for hormonal analysis (growth hormone, GH; insulin-like growth factor-I, IGF-1; insulin; and progesterone, P4) were obtained twice weekly for 40 days before artificial insemination for Japanese Black cattle and from 50 to 100 days postpartum for Holstein cows. Luteal phases were considered normal if the P4 concentrations for at least 3 time points over the course of 7 days remained above 1 ng/ml and at least 2 of the time points were above 2 ng/ml. The patterns of the ovarian cycles were classified into two types (normal or abnormal, such as having prolonged luteal phase and cessation of cyclicity) on the basis of the plasma P4 profiles. The plasma concentrations of IGF-1 in both breeds increased transiently during the preovulatory period when the P4 levels were low and decreased to lower levels during the luteal phase when the P4 levels were high. The plasma concentrations of insulin in the 3(rd) week of normal ovarian cycles when the plasma P4 concentration dropped to less than 1 ng/ml were higher than those at other time points in the Japanese Black cattle, but not in the Holstein cows. The plasma concentrations of GH did not change during the ovarian cycle in either breed. In conclusion, the present study indicates that the plasma IGF-1 concentration increases during the follicular phase (low P4 levels) and decreases during the luteal phase (high P4 levels) in non-lactating Japanese Black and lactating Holstein cattle. The results suggest that ovarian steroids, rather than nutrient status, may be related to the cyclic changes in IGF-1 secretion from the liver in cattle.  相似文献   

11.
Endocrine patterns were compared in 2 strains of Japanese black cattle with growth retardation; MHO- and HSK-paternal strains (MHO and HSK cattle, respectively). MHO cattle (n=8) displayed lower serum concentrations of insulin-like growth factor-1 (IGF-1), triiodothyronine (T3), thyroxine (T4), and cortisol (31.1+/-20.7 ng/ml, 73.9+/-51.9 ng/dl, and 2.9+/-2.9 microg/dl, 1.3+/-0.7 microg/dl, respectively) than those in both HSK cattle (n=5) (64.9+/-47.6 ng/ml, 97.8+/-40.7 ng/dl, 4.1+/-2.1 microg/dl and 1.8+/-1.1 microg/dl, respectively), and the controls (n=6) (314.7+/-197.2 ng/ml, 140.2+/-21.3 ng/dl, 5.8+/-1.7 microg/dl, and 3.0+/-1.4 microg/dl, respectively). The area under the concentration curve of growth hormone (GH-AUC 0-600 min) in MHO cattle (22210+/-18951 ng.min/ml) tended to be greater than those in HSK (7887+/-6340 ng.min/ml) and the controls (2811+/-1275 ng.min/ml). MHO cattle showed a high GH-AUC0-600 min in contrast to a low serum IGF-1 concentration, as well as lower serum T3, T4, and cortisol concentrations. HSK cattle exhibited the same secretory patterns, but much more moderately. Growth retardation in Japanese black cattle exhibits some variations based on pedigree.  相似文献   

12.
The objective of this study was to determine effects of age and castration on follicle stimulating hormone (FSH) secretion in prepuberal heifers. In experiment 1, twelve heifers were bilaterally ovariectomized at 3, 6, or 9 months of age (n = 4/group). Blood was collected at 10 min intervals for 8 hr at 1 week before ovariectomy and 1 and 4 weeks after ovariectomy. Frequency, amplitude and duration of FSH pulses were calculated. Mean plasma concentration of FSH (ng/ml), and frequency (pulses/8 hr), amplitude (ng/ml), and duration (min/pulse) of FSH pulses were not altered by age. Mean concentration of FSH increased (P less than .01) from 1 week before to 1 week and 4 weeks after ovariectomy, respectively, in all age groups. Pulse frequency increased (P less than .05) from 1 week before ovariectomy to 4 weeks after ovariectomy in 3 month old heifers, from 1 week before to 4 weeks after ovariectomy in 6 month old heifers, and from 1 week before to 1 week and 4 weeks after ovariectomy in 9 month old heifers. In experiment 2, twelve heifers were bilaterally ovariectomized at 3, 6 or 9 weeks of age (n = 4/group). Sample collection and measurement of mean concentration of FSH were the same as in experiment 1. Mean concentration of FSH increased (P less than .01) from 1 week before to 1 and 4 weeks after ovariectomy in heifers ovariectomized at 6 and 9 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

13.
OBJECTIVE: To determine norepinephrine (NE) kinetics in dogs with experimentally induced renal vascular hypertension. ANIMALS: 4 mixed-breed dogs. PROCEDURE: The study comprised a control and hypertensive period. The hypertensive period followed induction of renal vascular hypertension achieved by surgical placement of clips on both renal arteries to reduce diameter by approximately 80%. Arterial blood pressure, renal clearance, and NE kinetics were measured during each period while dogs were receiving a low-sodium diet. Measurements of NE kinetics and renal clearance during the hypertensive period were made 5 days after induction of hypertension. RESULTS: Five days after induction of hypertension, arterial blood pressure increased by 15 to 20 mm Hg. Mean (+/- SEM) plasma NE concentration and NE spillover rate increased significantly from 151.5+/-14.1 pg/ml and 8.03+/-0.62 ng/kg/min, respectively, during the control period to 631.4+/-30.5 pg/ml and 54.0+/-5.2 ng/kg/min, respectively, during the hypertensive period. Norepinephrine clearance rate also increased (54.0+/-2.4 vs. 86.0+/-9.3 ml/kg/min). Positive associations between mean arterial pressure (MAP) and NE concentration and spillover rate were detected. However, MAP and NE clearance rate were not associated. CONCLUSIONS AND CLINICAL RELEVANCE: Increased blood pressure during the hypertensive period was likely attributable to increased NE spillover rate, which resulted in a significant increase in plasma NE concentration. Analysis of these results suggests that central sympathetic outflow was increased and may be responsible for the pathogenesis of high blood pressure during the acute phase of renal vascular hypertension in dogs.  相似文献   

14.
Hypothalamic control of luteinizing hormone (LH) secretion was investigated in crossbred beef heifer calves by comparing anterior (AHD), posterior (PHD), and complete (CHD) hypothalamic deafferentation with sham operated controls (SOC). Heifers (n = 16) were fitted with an indwelling jugular catheter for 6 days before cranial surgery, and assigned randomly to treatments. Blood for radioimmunoassay of LH was collected sequentially at 15-min intervals during an 8-h period on days ? 1 before and day 6 after hypothalamic deafferentation or sham operation. On the day of surgery, blood samples were collected sequentially at 15-min intervals 2 h before induction of anesthesia and throughout surgery and early recovery. Seven months after hypothalamic deafferentation, all experimental and sham operated heifers were ovariectomized and treated with vegetable oil (i.m.) plus saline (i.v.), vegetable oil plus gonadotropin releasing hormone (GnRH), estradiol benzoate (EB, 1 mg) in vegetable oil. After ovariectomy basal plasma concentrations of LH increased (P < 0.01) compared with the low circulating hormone levels before ovariectomy. The amplitude of LH response to GnRH was greater (P < 0.01) in CHD and PHD when compared with SOC and AHD heifers. Injection of EB failed to induce a LH surge in CHD and PHD 900–1100 min later when compared with the robust response seen in SOC and AHD heifers. Injection of EB plus GnRH elicited LH release in all deafferentated and sham operated heifers. These results indicate a transient change in LH secretion after AHD or CHD in prepuberal heifers with intact ovaries. After OVX, the integrity of the neural connection of the posterior hypothalamus is required for EB-induced LH release in beef heifers.  相似文献   

15.
The effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given 100 microg of GnRH im were determined in three experiments. In Experiment 1, heifers were given GnRH 3, 6 or 9 days after ovulation; 8/9, 5/9 and 2/9 ovulated (P<0.02). Mean plasma concentrations of progesterone were lowest (P<0.01) and of LH were highest (P<0.03) in heifers treated 3 days after ovulation. In Experiment 2, heifers received no treatment (Control) or one or two previously used CIDR inserts (Low-P4 and High-P4 groups, respectively) on Day 4 (estrus=Day 0). On Day 5, the Low-P4 group received prostaglandin F(2alpha) (PGF) twice, 12 h apart and on Day 6, all heifers received GnRH. Compared to heifers in the Control and Low-P4 groups, heifers in the High-P4 group had higher (P<0.01) plasma progesterone concentrations on Day 6 (3.0+/-0.3, 3.0+/-0.3 and 5.7+/-0.4 ng/ml, respectively; mean+/-S.E.M.) and a lower (P<0.01) incidence of GnRH-induced ovulation (10/10, 9/10 and 3/10). In Experiment 3, 4-6 days after ovulation, 20 beef heifers and 20 suckled beef cows were given a once-used CIDR, the two largest follicles were ablated, and the cattle were allocated to receive either PGF (repeated 12h later) or no additional treatment (Low-P4 and High-P4, respectively). All cattle received GnRH 6-8 days after follicular ablation. There was no difference between heifers and cows for ovulatory response (77.7 and 78.9%, P<0.9) or the GnRH-induced LH surge (P<0.3). However, the Low-P4 group had a higher (P<0.01) ovulatory response (94.7% versus 61.1%) and a greater LH surge of longer duration (P<0.001). In conclusion, although high plasma progesterone concentrations reduced both GnRH-induced increases in plasma LH concentrations and ovulatory responses in beef cattle, the hypothesis that heifers were more sensitive than cows to the suppressive effects of progesterone was not supported.  相似文献   

16.
Bioavailability and pharmacokinetics of metoclopramide in cattle   总被引：1，自引：0，他引：1  
The bioavailability of metoclopramide was investigated in three steers following administration of 8 mg/kg by the oral, abomasal (cannula), and intravenous routes, using a Latin square design. The mean (± SD) oral and abomasal bioavailabilitles were 51.3 ± 30.7% and 76.2 ± 15.5%, respectively. The mean value for clearance ( C1 ) was 20.1 ± 5.9 ml/min and the volume of distribution ( V d) was 0.51 ± 0.19 1/kg. Additionalpharmacokmetic parameters for metoclopramide were determined following intravenous administration to seven cows. A predominate two-compartment model of distribution was found in six cows with a t 1/2α harmonic mean of 24.2 min and a range of 11.2–72.4 min, a t 1/2β harmonic mean of 53.1 min and a range of 31.1–134.1 min, a Cl of 42.2 ± 8.7 ml/min, and a V d of 2.1 ± 0.8 1/kg. To better define the relationship between metoclopramide concentration and release of prolactin, a treatment-by-subjects infusion study was conducted in which four different loading doses followed by constant infusion were used. A steady-state metoclopramide concentration ( MCP ss) of 8.8 ± 2.6 ng/ml was associated with a three-fold elevation of prolactin to a mean value of 12.1 ± 3.1 ng/ml in six yearling steers. Steady state serum prolactin concentrations ( PRL ss) did not rise significantly above 23.3 ± 6.9 ng/ml, even when MCP ss reached a concentration of 518.5 ±151.2 ng/ml. The short half-life, moderate V d, low minimum pharmacologically effective concentration, and rapid C1 found for metoclopramide in cattle in this study, suggest that a continuous release device could potentially be useful in the application of this drug in the prevention and treatment of fescue toxicosis.  相似文献   

17.
The effect of plasma from cyclic versus nutritionally induced anovulatory beef heifers was evaluated on proliferation of bovine granulosa cells in vitro. Granulosa cells were obtained from small (1-5mm) follicles of cattle and cultured for 4 days. During the last 2 days of culture, cells were exposed to medium containing 0, 1 or 10% plasma from cyclic or anovulatory heifers in the presence or absence of IGF-I (100ng/ml). Cell numbers were determined. Regardless of source, increasing percentage of plasma to culture medium increased cell numbers. However, the plasma-induced increase was greater in granulosa cells exposed to cyclic heifer plasma versus anovulatory heifer plasma. In addition, concomitant treatment with IGF-I dramatically improved cell proliferation induced by anovulatory heifer plasma. These results indicate that plasma from cyclic heifers contain factors that are a greater stimulus to granulosa cell proliferation than plasma from anovulatory heifers. Systemic factors such as IGF-I may play a role in directly regulating granulosa cell proliferation in cattle.  相似文献   

18.
To clarify endocrine responses to psychological stressors in cattle, the effects of isolation from familiar peers on plasma prolactin (PRL) and cortisol (CORT) concentrations, and the effect of 3,4‐dihydroxy‐L‐phenylalanine (L‐DOPA), a precursor of dopamine (DA), on stress‐induced PRL secretion were determined in Holstein steers. First, the potency of peripheral L‐DOPA administration on attenuation of central DA levels was confirmed. Cerebrospinal fluid (CSF) collected from a chronic cannula in the third ventricle and plasma were sampled 1 h before and 3 h after intravenous injection of L‐DOPA (100 mg/head). DA concentrations in CSF increased just after L‐DOPA injection with subsequent decrease in PRL secretion. Injection of L‐DOPA increased CORT secretion. Second, one experimental steer was isolated in its stall by removing its peers for 2 h with or without‐ pre‐injection of L‐DOPA. The concentration of PRL was elevated by isolation treatment, whereas the effect of isolation on CORT concentration could not be detected. The increase in PRL concentration after isolation was abolished by pre‐injection of L‐DOPA. These results suggest that PRL responds to isolation and that DA neurons in the central nervous system may regulate stress‐induced PRL secretion in steers.  相似文献   

19.
It has been reported that the posterior pituitary (PP) gland contains a potent, unknown prolactin (PRL)-releasing factor (PRF) in rats. PRFs are assumed to be produced in neurones located within the hypothalamus, and to be peptidergic in nature. However, little is known about PRFs in domestic animals. To characterize the PRF in the PP of domestic animals, the present study examined the PRL-releasing activity of an acidic extract from bovine PP (bPP) in vitro and in vivo in cattle. First, the PRL-releasing effect of bPP extract was compared with that of PRL-releasing peptide (PrRP), and thyrotropin-releasing hormone (TRH) from cultured bovine anterior pituitary cells. The extract significantly increased PRL concentrations in the culture medium, at doses of 0.002 and 0.02 eq./ml (one eq. is the PP extract from one animal), compared with the control (p < 0.05). PrRP failed to stimulate the release of PRL. TRH significantly increased PRL concentrations in the culture medium, at doses from 10(-9) to 10(-7) M, compared with the control (p < 0.05). The rate of increase in the PRL concentration, by 0.02 eq./ml bPP extract, was significantly greater than that in TRH (p < 0.05). Secondly, plasma PRL responses to the intravenous (i.v.) injection of bPP extract (0.5 eq./head), PrRP [3.59 mug/kg body weight (BW)], TRH (1 mug/kg BW), and a dopamine receptor antagonist (sulpiride, 0.1 mg/kg BW), were examined in calves. PrRP failed to stimulate PRL release; however, plasma PRL increased immediately following the injection of bPP extract, TRH and sulpiride. The PRL-releasing effect of i.v. injections of TRH and sulpiride was more potent than that of bPP extract. Finally, plasma PRL responses to the intra-hypothalamic injection of bPP extract were examined in calves. The intra-hypothalamic infusion (arcuate nucleus) of 0.0625 eq./head of bPP extract strongly stimulated PRL release in calves (p < 0.05). The present results show that PP contains a physiologically potent PRF in cattle.  相似文献   

20.
In veterinary medicine, dopamine is currently being administered clinically by infusion for treatment of kidney disorders at low doses (< or = 3 microg/kg/min) and for assessment of hemodynamics at high doses (> or = 5 microg/kg/min). However, since high doses of dopamine cause peripheral vasoconstriction due to its effect on alpha adrenoceptors, high doses have no longer been recommended. The present study was conducted to explore possible regimens for the use of dopamine infusion in dogs. The regional (renal and cardiac) blood flow for 60 min was measured by using colored microspheres at three doses (3, 10 and 20 microg/kg/min) of dopamine infusion in healthy anesthetized mongrel dogs. The effects on kidney and peripheral hemodynamics at each dose and the resultant cardiac output, mean arterial blood pressure and total peripheral resistance were determined. Renal blood flow increased markedly at 3 microg/kg/min dopamine. Improvement in hemodynamics indicated by marked increase in cardiac blood flow, cardiac output and mean arterial blood pressure and decreased total peripheral resistance was observed at higher doses (10 and 20 microg/kg/min). At 10 microg/kg/min, in addition to the satisfactory increase in cardiac blood flow, there was also a stable satisfactory increase in renal blood flow. However, at 20 microg/kg/min, increased myocardial oxygen consumption (manifested by marked increased in cardiac output), arrythmia and irregular increase in renal blood flow were detected. This study suggests that the clinical use of dopamine infusion in dogs could be safely expanded to moderately higher doses.  相似文献   

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